The study involved conducting a systematic review and meta-analysis of biomedical databases and other literature for studies concerning the risk of patients with type 2 diabetes who take thiazolidinediones (a class of drug that includes Actos, known generically as pioglitazone) developing bladder cancer. Researchers noted that patients with type 2 diabetes already have a 40 percent increased risk of developing bladder cancer. "Thiazolidinediones, especially pioglitazone, may increase the risk," they wrote.
Among the studies that previously suggested an increased risk of bladder cancer in patients who used pioglitazone was the PROactive (PROspective pioglitAzone Clinical Trial in macroVascular Events), although that risk was not considered significant. Other studies, however, provided conflicting results as to whether or not Actos was associated with a higher incidence of bladder cancer. The CMAJ study's authors wrote that some studies have reported, "a significant increase, a nonsignificant increase and even a decreased risk of bladder cancer."
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"Our results suggest an association between pioglitazone use and bladder cancer in adults with type 2 diabetes," researchers concluded. They noted that although the absolute risk of bladder cancer is small, there are other treatments for type 2 diabetes that may be just as effective as pioglitazone but do not come with the same risk of bladder cancer.